In the use of pneumatic conveying systems for transporting bulk materials to storage, transport or processing sites, the material typically is impelled by a pressurized gas and discharged into a closed compartment. Because of the pressurized air flow utilized in transporting the material, the collection compartment must be ventilated. Otherwise, the normal discharge of material into the compartment will be impaired if not entirely halted. Further because of the nature of some of such material which have a very fine particle size, such as titanium oxide, a portion of such materials become airborne and apt to be vented into the ambient atmosphere with the discharged air. Such escape of airborne material results not only in a contamination of the ambient atmosphere and possible harm to operating personnel but a wasteful loss of product. Accordingly, the principal object of the present invention is to provide a system for pneumatically conveying a bulk material and particularly a material very fine in particle size in which all of the material is deposited at the selected destination site without the loss of any airborne material. Another object of the present invention is to provide an apparatus for filling a container by gravity flow of material in which displaced air is vented and material entrained in vented air is captured.